Question 1

An object of mass $$M is at $$rest on an inclined ramp at angle $$	heta. $$Which of the following correctly expresses the magnitude of the normal force $$F_N$$ exerted by the ramp on the object?

Accepted Answer

$$F_N = Mg \cos 	heta$$

Question 2

A sled of mass $$m is $$pulled horizontally at constant velocity across a flat surface with kinetic friction coefficient $$\mu_k. $$What is the magnitude of the force you must exert to keep the sled moving at constant velocity?

Accepted Answer

$$F = \mu_k m g$$

Question 3

For an object at rest on an inclined plane, which force acts parallel to the surface and opposes the component of gravity down the ramp?

Accepted Answer

Friction force

Question 4

A skydiver of mass $$m$$ reaches terminal velocity $$v_t$$ during free fall. Which equation correctly relates $$v_t to $$the drag coefficient $$C_d$$, air density $$\rho$$, and cross-sectional area $$A$$?

Accepted Answer

$$v_t = \sqrt{\frac{2mg}{C_d \rho A}}$$

Question 5

If a skydiver opens their parachute and the drag coefficient increases by a factor of 5, what happens to their terminal velocity?

Accepted Answer

It decreases by a factor of $$\sqrt{5}$$

Question 6

Which of the following best describes the direction of pressure drag force acting on a moving object through a fluid?

Accepted Answer

Opposite to the direction of the object's velocity

Question 7

A box of mass $$m is at $$rest on a ramp inclined at angle $$	heta. If $$the coefficient of static friction is $$\mu_s$$, what is the minimum value of $$\mu_s$$ required to prevent the box from sliding?

Accepted Answer

$$\mu_s = 	an 	heta$$

Question 8

A skydiver jumps from a plane and falls freely for a distance $$\Delta y$$ before opening the parachute. Neglecting air resistance, what is the skydiver's velocity just before opening the parachute?

Accepted Answer

$$v = \sqrt{2g \Delta y}$$

Question 9

When pulling a sled at constant velocity, which statement is true about the net force acting on the sled?

Accepted Answer

The net force is zero

Question 10

A skier of mass $$m$$ slides down a frictionless ramp inclined at angle $$	heta. $$What is the skier's acceleration down the ramp?

Accepted Answer

$$a = g \sin 	heta$$

Question 11

A skydiver of mass $$m$$ reaches terminal velocity $$v_t$$ when the drag force equals the gravitational force. Which equation represents this balance?

Accepted Answer

$$\frac{1}{2} C_d \rho A v_t^2$ = m g$$

Question 12

If the coefficient of kinetic friction between a sled and the ground is $$\mu_k$$, and the normal force is $$F_N$$, what is the frictional force acting on the sled?

Accepted Answer

$$F_{fr} = \mu_k F_N$$

Question 13

A box is at rest on an inclined plane. If the angle of the incline increases, what happens to the normal force acting on the box?

Accepted Answer

It decreases

Question 14

A skydiver of mass $$m$$ falls at terminal velocity $$v_t. If $$the air density $$\rho$$ doubles, what happens to the terminal velocity?

Accepted Answer

It decreases by a factor of $$\sqrt{2}$$

Question 15

Which of the following is NOT a force acting on a sled being pulled horizontally at constant velocity?

Accepted Answer

Centripetal force

Question 16

A skydiver opens their parachute and the cross-sectional area increases. What is the effect on the drag force?

Accepted Answer

Drag force increases

Question 17

On an inclined plane, the component of gravity acting parallel to the surface is given by which expression?

Accepted Answer

$$mg \sin 	heta$$

Question 18

A skydiver of mass $$m$$ falls at terminal velocity $$v_t. If $$the mass doubles, what happens to the terminal velocity?

Accepted Answer

It increases by a factor of $$\sqrt{2}$$

Question 19

Which of the following is the correct expression for the pressure drag force on a large object moving through a fluid?

Accepted Answer

$$F_{drag} = \frac{1}{2} C_d \rho A v^2$

week 6 handout

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